Cost Price, Sales Price, Mark-Up

Q: How do you find the cost price if the sales are $216,000 and the mark-up is 50%?

A: "Mark-up" literally means the amount you "mark up" the cost by (the amount you increase it by) to get to the selling price. The percentage (50%) is based on the cost - i.e. the profit (mark-up) is 50% of the cost price.